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  • #31
    Originally posted by TGP37 View Post
    I bet if you tossed in a standard set of forged pistons with new rings capable of handling the heat from the turbo, along with a good cross hatching.....you will be happy. Then if you want more power, just up the boost more.
    Agree, that was my original plan. Just re-hone and install with new moly rings. But then I found this info about shaving the pistons. I've heard about it before but never on a GM 660. So I figured that if could take advantage of increased displacement without buying new pistons that would be great. Not to mention this hasn't been tried yet, well at least that I know of.

    I found the pistons info thread to confirm if forged slugs are in fact taller than cast and yes, it seems they are. Forged have 1.598 CD and Cast have 1.578 CD vs 1.442 CD for 3.1 (Iron Head).


    Now my question is, should I subtract the Compression Distance between the 3.1 and 2.8 forged pistons to find out how much should they be milled?

    Also, will the slash cut crankcase evacuation system be enough to help with rings break-in on whichever route I decide to go? Has anyone measured the amount of vacuum pulled with this system?

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    • #32
      Personally I would buy one piston first and have it milled, cut in half for a cross section and measured to make sure you have enough meat left to be safe. Just my $.02

      Sent from my HTC One X using Tapatalk 2
      -60v6's 2nd Jon M.
      91 Black Lumina Z34-5 speed
      92 Black Lumina Z34 5 speed (getting there, slowly... follow the progress here)
      94 Red Ford Ranger 2WD-5 speed
      Originally posted by Jay Leno
      Tires are cheap clutches...

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      • #33
        I hear ya...good thing is I don't need to buy 'em. Already have 8. 6 of them are installed in the low compression engine.

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        • #34
          Good deal. I would hate to see you pull your engine apart and toss 6 in not knowing how thick the crowns are and shatter 1 or 3.
          -60v6's 2nd Jon M.
          91 Black Lumina Z34-5 speed
          92 Black Lumina Z34 5 speed (getting there, slowly... follow the progress here)
          94 Red Ford Ranger 2WD-5 speed
          Originally posted by Jay Leno
          Tires are cheap clutches...

          Comment


          • #35
            Originally posted by pocket-rocket View Post
            Personally I would buy one piston first and have it milled, cut in half for a cross section and measured to make sure you have enough meat left to be safe. Just my $.02

            Sent from my HTC One X using Tapatalk 2
            Smart idea, but not surprised. You often have great advise.
            1996 Grand Prix | 3100v6 L82 | T04E-50 Turbo | Getrag 282 w/ EP LSD | SPEC-3 Clutch

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            • #36
              Originally posted by TGP37 View Post
              Smart idea, but not surprised. You often have great advise.
              Thanks. I try to think logically.

              Actually milling would be a waste of money. Just cut in half and measure, lol.

              Sent from my HTC One X using Tapatalk 2
              -60v6's 2nd Jon M.
              91 Black Lumina Z34-5 speed
              92 Black Lumina Z34 5 speed (getting there, slowly... follow the progress here)
              94 Red Ford Ranger 2WD-5 speed
              Originally posted by Jay Leno
              Tires are cheap clutches...

              Comment


              • #37
                Thanks, that is exactly what I'll end up doing.

                Now, regarding the slash cut crankcase evacuation system. Will it pull enough vacuum to help with rings break-in? Has anyone measured the amount of vacuum pulled with this system? Better yet, has anyone performed ring break-in procedure with this setup?

                My guess is the process would be different since the vacuum will be mostly generated during acceleration and not during engine braking.

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                • #38
                  Maybe Superdave will chime in on slash cuts. I'm not sure on vacuum numbers but I know his was generating enough to suck oil into the exhaust on acceleration, so I would run a catch can if you go that route.

                  Sent from my HTC One X using Tapatalk 2
                  -60v6's 2nd Jon M.
                  91 Black Lumina Z34-5 speed
                  92 Black Lumina Z34 5 speed (getting there, slowly... follow the progress here)
                  94 Red Ford Ranger 2WD-5 speed
                  Originally posted by Jay Leno
                  Tires are cheap clutches...

                  Comment


                  • #39
                    Look what the UPS man just delivered.



                    Got to love Summit Racing 2 day delivery upgrade.

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                    • #40
                      Slash cut: Works at idle well enough to keep from smoking. IIRC, if you can log your oil pressure you will see the pressure difference when unplugging the tube to the exhaust.

                      My oil psi dropped roughly 5-7 psi when I installed the slash cut. That tells me the system is pulling roughly 5-7 psi at idle.

                      I'm sure the crankcase and rings don't care what makes the vacuum source, just as long as there is a vacuum placed. In fact, you can get serious and install a stronger vacuum pump and really pull a vacuum worth more power. Ends up with less atmosphere for the crank to resist against, less oil suspended in a cloud around the crank, greater pressure difference across the rings.......some claim to pull a good amount of extra power with powered ventilation.
                      1996 Grand Prix | 3100v6 L82 | T04E-50 Turbo | Getrag 282 w/ EP LSD | SPEC-3 Clutch

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                      • #41
                        Some info on crankcase vac


                        Got Lope?
                        3500 Build, Comp XFI Cam 218/230 .050 dur .570/.568 lift 113LSA
                        Fully Balanced, Ported, 3 Angle Valve Job, 65mm TCE TB, S&S Headers.
                        Stage-1 Raybestos/Alto 4t60e-HD, EP LSD, 3.69FDR
                        12.61@105 Epping NH Oct 2015 Nitrous 100shot (melted plugs) 13.58@98.8 N/A 3200LBS

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                        • #42
                          Guys, it's been a while since I worked on my 60degreev6 car, been gathering parts for my tranny / engine rebuild.

                          I still have a compression concern and need your input before I jump on this, thus I'm reviving this thread from the dead.

                          Could the low compression numbers be due to my custom cam? Here are the numbers:


                          Duration @0.006 in
                          Intake 261
                          Exhaust 280

                          Duration @0.050 in
                          Intake 218
                          Exhaust 231

                          Lift at Cam
                          Intake 0.309
                          Exhaust 0.320

                          Lift at Valve w/ 1.5 Ratio Rockers
                          Intake 0.463
                          Exhaust 0.480

                          Timing at 0.050 in lift

                          Open
                          Intake BTDC -4
                          Exhaust BBDC 48

                          Close
                          Intake ABDC 42
                          Exhaust ATDC 2

                          Centerlines
                          Lobe Seperation 113
                          Intake Centerline 113

                          Overlap @0.006 in
                          45

                          Overlap @0.050 in
                          -2

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                          • #43
                            If you have stock pistons etc, your compression readings will be lower than an enigine with a stock cam. I have a simular cam, except your LSA is a lot wider. I am running 12 to 1 CR in mine. If you are running stock CR then I do think you will have a problem. Larry

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                            • #44
                              Looking at the numbers now, the exhaust open 48 degrees BBDC (mine is 19.4) seems really early, but that should not have any effect on the compression you see while cranking.

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                              • #45
                                Larry, thanks for replying.

                                I have stock size TRW forged slugs, they are a tad taller than stock, not more than 9.5 to 1 CR. This is a 2.8 gen 1 HO engine.

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